Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

How much make up air?

Hi,
I would love any help you could give me with regards to deciding how much make up combustion air i need for my master bedroom area. The natural gas, room air fed units are a 90% 80k btu furnace (oversized), and two (overkill) 50 gallon hot water heaters, in a 700 sq ft unfinished basement (insulated ceiling).

It connects via an open 3/4 door passage to an area where my wife works out (rarely i must add). There were two screens in place of concrete blocks for vents in the equipment room. In winter the equipment area is freezing cold, and the cold drifted over to my wife's workout area. I perhaps stupidly sealed off the two screen vent/holes.

I would love to have the minimum safe air possible. What would i need in winter? Maybe just one open. What about summer (only the hot water heaters).

Hi,
I would love any help you could give me with regards to deciding how much make up combustion air i need for my master bedroom area. The natural gas, room air fed units are a 90% 80k btu furnace (oversized), and two (overkill) 50 gallon hot water heaters, in a 700 sq ft unfinished basement (insulated ceiling).

It connects via an open 3/4 door passage to an area where my wife works out (rarely i must add). There were two screens in place of concrete blocks for vents in the equipment room. In winter the equipment area is freezing cold, and the cold drifted over to my wife's workout area. I perhaps stupidly sealed off the two screen vent/holes.

I would love to have the minimum safe air possible. What would i need in winter? Maybe just one open. What about summer (only the hot water heaters).

Well would two, or preferably one, screens instead of block be enough? (16x8 each i'm guessing). It would be about 25 feet away, and certainly not low and high.

I guess i wouldn't care if I could put a door to the room, but there are the water pipes and the water heaters. The room gets its heat passively mostly from the other room, (which gets it from lack of insulation b/t the study above). A stupid arrangement.

Perhaps not relevant, but the space is 1,000 sq ft (maybe 1500 is you include the non-insulation/drift to part of the basement.) So the furnace is only running in short bursts. The hot water heaters are for the "whirlpool" tub, which is never used, and the over the head huge shower rain-like head, also never used. It looks great in the ads, but water pouring straight down runs over the face and eyes, really not pleasant. But I guess it might be used so I should plan enough air for them both on full draw.

dan sw fl:
Thanks! 1995 construction, w/dryvit on the exterior walls (super tight), but no spray foam or anything special in the attic or basement area. Would you agree that i'm "not unusually tight".

If that's the case, i could leave it as is, no outside air. The 3/4 door size passage way is more than 1 sq inch/1k btu. To be safe may I will leave a 7x7 inch opening in the block screen (1 sq/4k btu).

dan sw fl:
Thanks! 1995 construction, w/dryvit on the exterior walls (super tight), but no spray foam or anything special in the attic or basement area. Would you agree that i'm "not unusually tight".

If that's the case, i could leave it as is, no outside air. The 3/4 door size passage way is more than 1 sq inch/1k btu. To be safe may I will leave a 7x7 inch opening in the block screen (1 sq/4k btu).

Thanks

Steve

Thanks.

You should be fine as is since the room communicates with the rest of the basement, and you could pipe the intake to the furnace to the outside as a quick reduction .